The present invention relates to a process for the preparation of hydrogen peroxide. More particularly, the present invention relates to a process for the preparation of hydrogen peroxide by hydrogenating 3-2-(oxopropyl)-2(1H)-quinoxalinone in the presence of a palladium catalyst and contacting the 3-2-(oxopropyl)-1,2,3,4-tetrahydro-2-quinoxalinone with oxidant molecular oxygen or air in ethylacetate-water or chloroform-water biphasic system.
Hydrogen peroxide is one of the most important oxidising agents and is widely used in industry. Currently, the United States alone produces almost about 700000 tons of hydrogen peroxide. A substantial amount of hydrogen peroxide is used in the paper and pulp industry, waster disposal management, preparation of peroxygen compounds and as non-polluting environment friendly oxidising agents in chemical industry. The dominant current route to produce hydrogen peroxide from hydrogen and oxygen is the xe2x80x98anthraquinone autoxidation processxe2x80x99 which requires extraction of hydrogen peroxide by demineralised water from the reaction mixture in a separate step. Further, the hydrogen carrier 2-alkyl anthraquinone on hydrogenation produces several side-products such as hydrogenated aromatic rings, anthrones, tetrahydroalkylanthraquinone epoxide and the like [Kirk-Othmer Encyclopedia of Chemical Technology, 1996, 4th ed., 13, 968-969].
It is also known to prepare hydrogen peroxide by xe2x80x98alcohol autoxidationxe2x80x99. This route produces hydrogen peroxide by autoxidising isopropyl alcohol with oxygen enriched air in the range of 70-160xc2x0 C. and 10-20 atm. The coproduct acetone is catalytically reduced back to isopropyl alcohol. The disadvantage of this route is that it requires drastic reaction conditions and high capital investment, and a complex product and catalyst recovery scheme [Kirk-Othmer Encyclopedia of Chemical Technology, 1996, 4th ed., 13, 976-977].
In the xe2x80x98ARCOxe2x80x99 process, methylbenzyl alcohol (sec.phenylalcohol) is oxidised by molecular oxygen in liquid phase, giving acetophenone and hydrogen peroxide. The acetophenone is hydrogenated back to methylbenzyl alcohol. Here the formation of organic hydroperoxides is a concern and the oxidation requires drastic conditions such as temperature xcx9c160xc2x0 C., atmosphere xcx9c10-20 atm. of air or oxygen [Kirk-Othmer Encyclopedia of Chemical Technology, 1996, 4th ed., 13, 977].
Hydrogen peroxide has also been prepared by the aerobic oxidation of sec.alcohols catalysed by N-hydroxyphtalimide (NHPI) at a temperature of 75xc2x0 C. During this process, NHPI is partially converted to phthalimide [T. Iwahama, S. Sakaguchi, Y. Ishii, Org Procs. Res. and Devl, 2000, 4, 97-98].
It is also known to prepare hydrogen peroxide by reacting hydrogen and oxygen with a Pt/Pd salt to produce an aqueous solution of hydrogen peroxide. The reaction conditions required are high pressure of hydrogen fees (140 kg/cm2) and low temperature (10-17xc2x0 C.) [Kirk-Othmer Encyclopedia of Chemical Technology, 1996, 4th ed., 13, 977].
It is known to react carbon monoxide oxygen and water in the presence of palladium compound to obtain hydrogen peroxide by a non-hydrogen route. This reaction however, requires drastic conditions such as CO under 600 kPa and O2 under 6500 kPa partial pressure and also the presence of CF3COOH, etc [C. Shen, et al, J. Am. Chem. Soc., 2000, 122, 4029; R. Bortolo, et al, EP 788,988, Chemical Abstract, 1997, 127: 178353w; R. Bortolo et al, J. Mol. Catal. A: Chem., 2000, 153, (1-2), 25, Chemical Abstract, 2000, 132:224425z; D. Bianchi, et al, Angew Chem., Int. Ed., 1999, 38, 706 and W. Thiel, Angew. Chem., Intl. Ed., 1999, 38, 3157].
It is therefore important to devise and develop improved processes for the production of hydrogen peroxide which overcome the disadvantages of the prior art listed above.
The main object of the present invention is to provide a simple method for the production of hydrogen peroxide, which can be carried out at room temperature.
It is another object of the invention to provide a economical process for the production of hydrogen peroxide.
It is yet another object of the present invention to provide a process for the production of hydrogen peroxide where the hydrogen carrier and the solvent can be easily separated from the reaction mixture and recycled.
It is a further object of the invention to provide a process for the production of hydrogen peroxide where the work up of the product is simple.
The above and other objects of the invention are achieved by the process of the invention. To the best of the applicants"" knowledge, no prior art discloses the direct production of hydrogen peroxide from hydrogen and molecular oxygen or air at mild conditions without requiring expensive engineering costs and operational risks associated with separation of hydrogen peroxide.
Accordingly, the present invention relates to a process for the preparation of hydrogen peroxide comprising (a) hydrogenating compound of formula I below 
wherein R1 is selected from CH3, C2H5 and C6H5 and R2 is selected from the group consisting of H and CH3 provided that when R1 is C2H5 or C6H5, R2 is H, in the presence of a palladium catalyst to obtain compound of formula II; 
wherein R1 is selected from CH3, C2H5 and C6H5 and R2 is selected from the group consisting of H and CH3 provided that when R1 is C2H5 or C6H5, R2 is H, and (b) contacting the compound of formula II so obtained with an oxidant selected from the group consisting of molecular oxygen, air and a mixture thereof in a biphasic system selected from ethylacetate-water and chloroform-water systems to obtain hydrogen peroxide.
In one embodiment of the invention, the compound of formula I is selected from the group consisting of 3-2-(oxopropyl)-2(1H)-quinoxalinone, 3-2-(oxobutyl)-2(1H)-quinoxalinone and 3-2-(oxophenyl)-2(1H)-quinoxalinone to obtain 3-2-(oxopropyl)-1,2,3,4-tetrahydro-2-quinoxalinone, 3-2-(oxobutyl)-1,2,3,4-tetrahydro-2-quinoxalinone and 3-2-(oxophenyl)-1,2,3,4-tetrahydro-2-quinoxalinone respectively of formula II.
In another embodiment of the invention, the compound of formula II is contacted with oxidant in the presence of an organic solvent selected from the group consisting of benzene, ethyl acetate, chloroform, dichloromethane and tert.butyl alcohol.
In another embodiment of the invention, the compound of formula II is contacted with oxidant in the presence of a mineral acid, such as dilute sulphuric acid.
In another embodiment of the invention, the reaction is carried out at ambient temperature.
In another embodiment of the invention, compound of formula II is prepared from compound of formula I in the presence of Pd (10%)-carbon-H2(30-40 psig) or Pd (5%)-carbon-H2(30-40 psig).
In yet another embodiment of the invention, the hydrogenation pressure is in the range of 10-100 psig, preferably 20-40 psig.
In another embodiment of the invention, the product is obtained as an aqueous solution by removal of coloring materials from the water layer using activated carbon.
The process of the invention involves hydrogenating compound of formula I in the presence of a palladium catalyst to obtain compound of formula II. This is then taken in a biphasic system comprising ethylacetate-water or chloroform-water and contacted with an oxidant selected from molecular oxygen or air or a mixture of the two under suitable reaction conditions. If desired a mineral acid such as dilute sulphuric acid can be added. The water layer is separated using a separating funnel and the coloured material in the water layer removed using activated carbon to obtain aqueous solution of hydrogen peroxide.
The compound of formula I is selected from the group consisting of 3-2-(oxopropyl)-2(1H)-quinoxalinone, 3-2-(oxobutyl)-2(1H)-quinoxalinone and 3-2-(oxophenyl)-2(1H)-quinoxalinone to obtain 3-2-(oxopropyl)-1,2,3,4-tetrahydro-2-quinoxalinone, 3-2-(oxobutyl)-1,2,3,4-tetrahydro-2-quinoxalinone and 3-2-(oxophenyl)-1,2,3,4-tetrahydro-2-quinoxalinone respectively of formula II.
The process can be conducted over a wide range of temperature (between 10-100xc2x0 C., preferably between 20-40xc2x0 C.) and pressure (between 10-100 psig, preferably between 20-40 psig).
Preferably the reaction is carried out under conditions outside the explosive range for the temperature, pressure and oxygen concentration. It is ideal to carry out the reaction under ambient conditions of temperature and pressure.
The hydrogen carrier amide compounds used in the process are regeneratable. Preparation of these compounds is described in M. Goswami and N. Borthakur, Ind. J. Chem., 25 B, 525, 1986 and also in S. S. Nikam, A. D. Sahasrabudhe, R. K. Shastri, S. Ramanathan, Synthesis, 1983, 2, 145-146.
The following reaction scheme describes a preferred mode of performing the process of the invention: 
The process of the invention are described in the following examples, which are illustrative and should not be construed as limiting the scope of the invention in any manner.
Preparation of Hydrogen Peroxide